1. Field of the Invention
The present invention relates generally to jar assemblies and, more particularly, to a hydraulic jar apparatus (jarring tool) and method that operates to effect an axially directed jar impact without the requirement to reciprocate the wellbore string, e.g., the pipe or coiled tubing to which the jarring tool is attached.
2. Description of the Background
Coiled tubing is used in almost every area of oil and gas well operations from drilling operations to workovers. Because of the economy of operation and the convenience of moving a coiled tubing unit as compared to moving a drilling or workover rig, coiled tubing technology is increasingly used to replace rig operations in many areas, especially in remote areas. Coiled tubing may also be used for many specialized purposes such as gas injection or fishing operations.
During coiled tubing operations, various downhole tools are utilized, including jars for removing objects that may become stuck within the wellbore. For instance, expensive bottom hole assemblies including measurement-while-drilling (MWD) tools, bits, drill collars, stabilizers, jar sections, and the like, frequently become stuck in the wellbore.
Presently available jar apparatuses, including hydraulic jar apparatuses, require that the string be reciprocated to effect a jar impact. When operating a jar apparatus by reciprocating coiled tubing, the coiled tubing experiences bending cycles that introduce plastic strain and fatigue as the tubing is transferred from the storage reel to the wellbore. Although the surface components of the coiled tubing units, such as the injector head, tubing guide, and service reel, may be designed to extend the life of the coiled tubing, fatigue failure eventually occurs due to transfer of the coiled tubing from the storage reel to the wellbore. Fatigue failure occurs more rapidly if repeated high strains are imposed in combination with internal pressure within the coiled tubing. Fatigue failure may also be exacerbated by corrosion that may occur due to corrosive fluids, hydrogen sulfide, carbonic acid, saturated salt solutions, and the like. Additionally, coiled tubing strain may occur due to borehole geometry and deviation, pipe and tool weight, wellbore pressure, and frictional effects of tubing rubbing against casing or openhole.
In many instances, to effect recovery of a stuck tool, it is necessary to actuate the jar by reciprocating the pipe string many times. While coiled tubing is typically designed to be safely reciprocated thousands of times without failure, any failure of the coiled tubing that does occur is likely to be catastrophic. Coiled tubing failure can lead to costly loss of equipment and loss of the well, and/or cause human injury.
Because of the danger of coiled tubing failure, coiled tubing operators have a standard operating procedure of permitting only a certain number of reciprocations over a particular region of the tubing before the tubing is pulled from the wellbore. In fact, some experts recommend permitting only as few as ten reciprocations, depending on the conditions of the operation, before the tubing is pulled from the wellbore. The operator then cuts off a portion, generally about fifty or more feet, of the bottom section. The tubing is then run back into the well to continue operations with a relatively new section of coiled tubing positioned in the particular region where higher stress occurs. This procedure takes considerable time and must be repeated as necessary thereby greatly increasing the cost of the operation.
Both coiled tubing units and drilling rigs are used to drill horizontally extended reach wells, both onshore and offshore, that are now common operations all over the world. The bottom hole assembly (BHA) employed in such drilling operations may consist of a downhole motor, several nonmagnetic drill collars, an MWD tool, and other equipment. A drilling jar is usually run in the top section of this assembly. During the drilling operation, it is not uncommon for the BHA to become stuck, as discussed hereinbefore. Repeated jarring may not free the BHA and, in fact, the jar itself may become stuck or inoperable. It would be desirable to be able to continue jarring regardless of whether the BHA is stuck. It is also desirable to avoid reciprocating the coiled tubing during the jarring to avoid stress applied thereto as discussed hereinbefore. As well, coiled tubing may be used in fishing/workover operations to jar a stuck fish (downhole assembly of some type) from a well bore either in open hole or cased hole.
With standard pipe strings comprised of separately threaded pipes operable with a drilling or workover rig, it may be desirable to have the option to actuate a jar that is in a part of the pipe string below the stuck point or region. A jar apparatus positioned below the typical stuck point cannot be actuated because the pipe below the stuck point cannot be reciprocated.
In some cases, it would be desirable to position a jar in a portion of the bottom hole assembly that is more likely to become stuck, if the operator can be fairly certain it will be possible to actuate the jar regardless of whether the pipe can be reciprocated. In some cases, more than one jar is included in the pipe string, and it may be desirable to have the option to conveniently control each jar independently.
Another problem sometimes associated with the jar apparatus is the need to maintain a flow path therethrough. Because the jar apparatus typically includes relatively heavy and/or thick, axially movable bodies capable of withstanding large impacts, the provision of a flow path through the jar apparatus is an engineering problem for each jar design and especially for a hydraulic jar that has limited internal surface area for applying hydraulic pressure. It is desirable that the internal diameter of the flow path be as large as possible to allow passage of various wireline tools. At a minimum, the internal diameter should allow passage of a drop ball or other dropped member, to actuate release tools that are provided below the jar, such as a hydraulic disconnect.
Furthermore, it is desirable that a jar for use with coiled tubing be of relatively short length so that it can be accommodated within the length of a lubricator used to contain wellbore pressure. The jar design of the present invention allows adaptation to a short length if necessary but also allows a longer relative length of the jar if no length restrictions are desired. As well, it is desirable that the jar apparatus be easily transportable.
U.S. Pat. No. 4,545,444 and U.S. Pat. No. 3,627,356, which patents also designate the present inventor, are directed to a Jar Mechanism Energizer and a Directional Drilling Apparatus with Retrievable Limiting Device, respectively, and are each incorporated herein by reference.
Consequently, there remains a need for a jarring tool and assembly that offers dependable operation whether contained in the BHA below the stuck point or not, and without the need to reciprocate the string. Ideally, the jarring assembly should be relatively short and easy to transport. Those skilled in the art have long sought and will appreciate that the present invention provides solutions to these and other problems.